The invention relates to an electric cable cutter for cutting a wire such as an electric wire, and more particularly to a portable electric cable cutter in which a wire or the like is cut via a gear reduction (speed change) mechanism by means of an electric motor which is powered by a battery.
When a cable is cut or wires of various diameters are cut in an electric facility work, or when a steel bar is cut in an ironworks, a construction work, or the like, a cable cutter is used. Cable cutters of the prior art include a hydraulic cable cutter, and a manual tool which uses a toggle mechanism. The assignee of the present patent application proposed an electric cable cutter of the battery type which is shown in FIG. 8 (Japanese patent application No. HEI5-146935). Specifically, the electric cable cutter comprise: a case 61 which houses a planetary gear speed change mechanism; a battery cartridge 62 which is detachably mounted in the lower portion of a handle 61a of the case 61; a stationary blade 66 which is fixed to the case 61; and a rotary blade 67 which is rotatably attached to a bolt 65 at an end portion of the stationary blade 66 and which has a sector gear 67b in the outer side.
The electric cable cutter is used in the following manner. The worker grasps the handle 61a by one hand so as to set the rotary blade 67 free. A wire to be cut (hereinafter, such an object to be cut or worked is referred to as a work piece) is placed inside the stationary blade 66. The rotary blade 67 is rotated by hand so that an end portion of the gear 67b engages with a driving gear 63 of the final stage of the planetary gear reduction mechanism housed in the case 61. When a switch lever (not shown) is then pressed, the work piece is cut by a high rotational torque. The electric cable cutter is convenient to use because it can be operated by one hand and it does not require a force to be exerted by an arm.
The above-mentioned electric cable cutter is configured so that the driving gear 63 of the final stage of the planetary gear reduction mechanism housed in the case 61 meshes with the gear 67b of the rotary blade 67. Since the sector gear 67b is a large gear, the length L1 or the central angle 1 of the arc of the sector gear 67b of the rotary blade 67 which arc elongates from the start of the meshing state with the driving gear 63 to the end of the state are inevitably made large. Therefore, the time period of the cutting work tends to be prolonged. Although a large driving force is required at the initial period of the cutting work, a smaller driving force is required as the cutting work advances. In the cutter of the prior art, the same meshing state is maintained from the start of the cutting work to the end and hence a slightly unstable state is produced.
Furthermore, work pieces which are to be cut by an electric cable cutter include those of various kinds ranging from a thin wire member to a thick and hard piece. If the cutting work is performed with a rotational torque corresponding to the kind of the work piece, the work can be efficiently done. In the case where a work piece is so hard that it is hardly cut, there are fears that an excessive torque repulsion force is exerted and the electric motor is overheated, and that the battery is over-discharged and the life of the battery is shortened.